11
6072-2021
Power budget
The LD-63B is developed for Manchester coded protocols and this means that the power
budget will change with the number of preamble bits in the actual protocol. Preamble bits
are sent before the actual data and has the function of synchronise units in the network
(see figure below).
The LD-63B uses the preamble bits for stabilising before receiving data and this means that
the LD-63B will distort the preamble bits used with more than 10%. The diagrams shows the
available power budget at different number of available preamble bits and at different trans-
mission speeds.
Observe that the diagrams state the
minimum guaranteed power budget.
Experience show however that the typical
value is about 4 dBm higher with 820 nm,
about 3,5 dBm higher with 1300 nm and about 6 dBm higher with singel mode.
Also observe that the calculated values applies between two LD-63B units. In larger networks
each fiber optical loop needs to be summated to get the number of used preamble bits.
Example:
Calculation of number of used
preamble bits.
Assume 820 nm units and 1 Mbit/s tranmission rate.
This means that fiberloop 1, which need 6 dB, will use maximum 1 preamble bit
(from diagram).
Fiberloop 2 needs 14 dB and will use maximum 10 preamble bits (from diagram).
This gives a total maximum of 11 preamble bits.
Idle line
3 preamble bits
Start sending data
(Manchester coded)
LD-63B
Loop 1
6dB
14dB
Loop 2
LD-63B
LD-63B
Connection:
AUDIN - 8, avenue de la malle - 51370 Saint Brice Courcelles - Tel : 03.26.04.20.21 - Fax : 03.26.04.28.20 - Web : http: www.audin.fr - Email : [email protected]
